Field of the Invention
The invention concerns a cable for suspending a down hole pump in a well bore. The cable may also be usable for other applications such as fluid sampling and geophysical applications.
Description of Related Art
A cable to be used down hole needs to fulfill complex requirements; the cable should be of light weight and have a small diameter. Further, the cable will be employed at high temperatures, in one embodiment about 170° C. Consequently the cable structure must be provided to withstand the impact of high temperature without severe deterioration of the mandatory structural and functional features of the cable for fulfilling the specific use of the cable.
When using the cable for suspending a down hole pump, the cable must have structural provisions for enduring excessive tensile loads and high external pressures.
During down hole use the cable is exposed to aggressive chemicals and dissolved gases such as CO2 and H2S. The gases present in the environment of the bore hole tend to diffuse into voids in the cable and may accumulate in internal voids in the cable. This effect is especially pronounced at elevated temperatures. Such accumulated gases represent a potential hazard to the cable, and if the external pressure is reduced rapidly, for instance during retrieval of the cable or during adjustment of the borehole pressure the gases will expand and may cause damage to the cable.
Prior art publications relevant to the invention have been identified; U.S. Pat. No. 5,086,196 WO 2011106513, EP 2204823, U.S. Pat. No. 3,832,481.
U.S. Pat. No. 5,086,196 discloses an electro-mechanical cable for deploying pumping systems. The cable has a core comprising insulated conductors embedded in an elastomer core jacket which protects the conductors from mechanical damages as well as joining the conductors with the core jacket as a unit. A containment layer is wound on the core jacket in order to prevent outward radial expansion. An armour layer comprising helically wounded armour wires surround the containment layer and provide the axial strength to the cable.
WO 2011106513 discloses a cable with three conductors included in the core and a jacket layer surrounding the core. Plural wires for the provision of strength to the cable are positioned around the core outside the jacket layer. The wires are arranged with gaps filled with a polymer material in between the wires in the circumferential direction.
EP 2204823 shows an electro-mechanical cable with a core including conductors, wherein the core is encircled with an armour sheath comprising two layers of steel armour. The two armour layers comprises a plurality of interlocking strands wherein the surface of the strand is configured so that it matches the surface of a neighbouring strand for a locking effect. The armored layer provides axial strength to the cable as well as functioning as an anti-compression ring for resisting compression of the cable. A conduit for transport of fluid may be included in the electromechanical cable.
U.S. Pat. No. 3,832,181 shows a cable comprising conductors and the presence of various kinds of polymer for making up the layers of the cable.